Saturday's event drew visitors from across the state to the dam, which is on the Salt River northeast of Phoenix. Many had deeper ties to the structure, some going back generations.

Linda Pearce, 68, has seen the dam through decades of change. Her grandfather used to tell her stories about carrying building supplies for the dam by horse and wagon in the early 1900s.

Her husband worked as a safety engineer when Roosevelt Dam underwent a major modification in the 1990s: Its walls were raised 77 feet to provide for additional flood control and water-conservation storage space. The reconstruction was completed in 1996.

On Saturday, Pearce pointed to the water line, to remnants of an old gravel road that had looped around the mountains up to the dam itself, before the Roosevelt Lake Bridge was built in 1990.

"Before they did the remodeling, we used to drive over the old dam, and it was scary as heck," she said. "There was miles of dirt road that just wound in and out, and it was pure dust and the kids were always carsick and the whole thing."

Her children grew up boating, hiking and waterskiing around the dam. Now, her grandchildren visit and play there, too.

"The dam has been kind of a livelihood for my family," said Pearce, who lives halfway between Globe and Miami, about 30 minutes from the dam.

Other visitors came just to admire the engineering marvel, curious for the rare opportunity to stroll the 1,210 feet of the dam crest. The top of Roosevelt Dam was closed to the public for security reasons after Sept. 11, 2001, said Salt River Project spokesman Jeff Lane.

Adam and Leelannee Godfrey of Mesa stopped by the dam after a family camping trip in the Superstition Mountains.

Atop the structure, they hoisted their daughters, ages 3 and 7, above the cement walls so they could peer down at the water rippling below. They oohed and aahed at the carp flitting beneath the surface.

"I think there's a lot of historical significance to a centennial, something that predates the state," said John Felty, 46, of Gilbert, who went to the dam with a group of 10 relatives and friends.

Officials said 775 visitors toured the top of the dam Saturday, more than expected.

On one end of the dam, archaeologist Bryan Lausten condensed what normally was a 45-minute presentation about the dam's history to five minutes. Behind him was a display board pinned with black-and-white photos from 100 years ago, many showing a smiling, bespectacled former President Theodore Roosevelt at the dam's dedication ceremony on March 18, 1911.

On the other end, SRP engineer Paul Hursh spoke about the 1990s modification to dozens of groups.

As Sandy Warbington, 63, strolled the top of the dam, she reminisced about working on that modification. One of the jobs she remembered most clearly was operating a high-pressure "water broom" to wash chemicals off of the cement.

It was hard work, she said, and she was one of the few women who worked on the project.

"That's why I wanted to come here, to remember all the blood and sweat that I used to put into this place," Warbington said, rolling up her sleeves. "See all these scars? That's all from working here."

After Saturday, the top of the dam will be again closed to the public, likely until the next major anniversary.

Warbington seemed satisfied as she walked away from the dam, back to the shuttle bus waiting to take the group back to the visitor's center.

"I've had a few accomplishments in my life," she said, "but this is the one I want them to write on my obituary - that I worked on the dam."